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  • Title: Pharmacodynamic interaction of nitrous oxide with sevoflurane, desflurane, isoflurane and enflurane in surgical patients: measurements by effects on EEG median power frequency.
    Author: Röpcke H, Wirz S, Bouillon T, Bruhn J, Hoeft A.
    Journal: Eur J Anaesthesiol; 2001 Jul; 18(7):440-9. PubMed ID: 11437872.
    Abstract:
    BACKGROUND AND OBJECTIVE: This study investigates the interaction of sevoflurane and nitrous oxide on EEG median power frequency of 2.5 Hz during surgery. METHODS: Sevoflurane concentrations required for electroencephalographic median power frequency between 2 and 3 Hz were measured in 25 patients during gynaecological laparotomies. Nitrous oxide was randomly administered at 0, 20, 40, 60 and 75 vol%, subsequently two different concentrations in each patient. The data were analysed using isobolographic analysis together with previously published data on nitrous oxide-isoflurane, -enflurane, or -desflurane interaction. RESULTS: The interaction is described by the equation: C volatile anaesthetic/C0 volatile anaesthetic + C N2O/C0 N2O=1 (C is the concentrations for a drug combination to achieve the desired effect; C0 is the concentration for single drug use). The parameters are C0 isoflurane=1.11 vol% (95% CI 1.03-1.19), C0 enflurane=1.64 (1.52-1.77), C0 desflurane=5.31 (4.92-5.73), C0 sevoflurane=2.12 (1.96-2.29), C0 N2O=174 (153-202). These parameters decrease by 6% (2.5-10) for every 10 years of patients' age > 40 years. CONCLUSIONS: The interaction is compatible with additivity. The potency of nitrous oxide to substitute the volatile anaesthetics is less than anticipated from previously reported MAC values.
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